1. Field of the Invention
The present invention relates to a compressed television signal recording and reproducing apparatus for recording television signals compressed by means of a high efficiency compression algorithm and for reproducing the compressed television signals to a decoder.
2. Description of the Prior Art
High efficiency digital coding technologies for video and other image signals have progressed significantly in recent years. Particular attention has been given to inter-frame predictive coding techniques as a means of reducing redundancy on the time-base axis, and international standards for video signal coding techniques have been established. One of these is the ISO-13818 specification, which is commonly known as MPEG-2 for the Motion Picture Expert Group of the ISO.
This method reduces redundancy on the time base by inter-frame predictive coding, and reduces redundancy on the spatial base by discrete cosine transformation (DCT) coding. Predictive error is reduced by motion compensation during inter-frame prediction to improve coding efficiency. The coded data is generally recorded using variable length block units, macro block units, MBS units, picture units, and group-of-picture (GOP) units.
Systems for combining and packetizing the video and audio coded data in an MPEG signal have been established as a means of transmitting such variable length coded data. In this system, the coded data is first converted to variable length packets called a "packetized elementary stream" (PES); these PES packets are then divided into fixed length packets called the "transport stream packets" (TSP). Auxiliary information used, for example, to synchronize the audio and video or to identify multiplexed programs is also written to the TSP.
As described in An experimental study on a home-use digital VCR (IEEE International Conference on Consumer Electronics, Jun. 6-9, 1989; WPM8.6), when recording a base band signal in a digital video cassette recorder (DVCR), the input video signal is compressed, then an error correction signal is added to the compressed video signal for coding the signal for recording, and the coded signal is then recorded on a magnetic tape. During reproduction, the signal read from the magnetic tape is detected and processed for error correction, and then decoded to output the video signal. Note that the video signal is recorded to the magnetic tape in fixed length packet units.
When an MPEG or other compressed television signal is recorded and reproduced, the signal is packetized in units of a fixed number of bits in the transmission sequence of the signal sent from the encoder. During reproduction, the read-out packets are reconnected in the sequence to reproduce the original signal, which is then transmitted to the decoder.
With this conventional method, however, the following problems develop when the input data is data compressed by inter-frame coding as in the case of MPEG signals.
Specifically, during fast forward, fast reverse and other special reproduction modes, since a reproducing head scans across the recording tracks, it is impossible to reproduce frame data or to reproduce auxiliary signals necessary for the decoder to perform the decoding operation.
Secondly, it is also impossible to know contents of individual portions of a recording tape which are recorded on the tape over, for example, two hours or so.